Abstract
Mycobacterium avium subspecies paratuberculosis (MAP) is a bacterium that can cause substantial economic losses in infected dairy herds due to reduced milk production and increased cow-replacement costs. In order to control MAP in dairies with drylot pens, a standardized environmental sampling protocol to quantify MAP in fecal slurry was developed based on an existing protocol for freestall pens. Specifically, following a 24 h hold of the flush, a grab sample of approximately 10 ml of fecal slurry was collected every 1 m along the flush lane of the drylot pens, avoiding individual cow fecal pats. To determine the reliability and repatability of the new environmental sampling protocol for estimation of MAP bioburden at the pen level, two collectors simultaneously collected fecal slurry samples every day for 3 days from six drylot cow pens on two Central California dairies. During the study period no cow movement between pens was allowed with the exception of sick cows. The study herds had MAP seroprevalence of 5.8% and 3.2%, respectively, based on whole pen serum ELISA results. Variance components models for quantitative real-time PCR (qPCR) results showed samples collected from different pens on different dairies accounted for greater variablitiy in MAP concentration (65%), while samples collected by different collectors had the least variability (0.1%). In contrast, variability in MAP concentration in environmental samples collected on different days had 25% variability. The intraclass correlation coefficient showed high reliability (93%) of environmental sampling simultaneously by different collectors. In contrast, the reliability of environmental sampling at different days was 65%, which was similar to the reliability for sampling by different collectors on different days. Investigators can expect high reliability when employing the new environmental sampling protocol along with qPCR testing of environmental samples from drylot pens.
Highlights
Mycobacterium avium subspecies paratuberculosis (MAP) is an intracellular bacterium that causes a chronic granulomatous enteritis in ruminants commonly known as Johne’s disease
Herd 2 was a mixed breed herd composed of 2,733 lactating Jerseys and 1,188 lactating Holsteins housed in drylot and freestall pens and was not routinely tested for MAP
Findings from the study show that environmental sampling using the standardized sampling protocol described followed by testing of samples by quantitative real-time PCR (qPCR) can reliably quantify MAP bioburden at the pen level on drylot pens even when implemented by different collectors, at different times, and up to 3 days apart
Summary
Mycobacterium avium subspecies paratuberculosis (MAP) is an intracellular bacterium that causes a chronic granulomatous enteritis in ruminants commonly known as Johne’s disease. Johne’s disease can cause substantial economic losses in infected dairy herds due to reduced milk production (Aly et al, 2010) and increased cow-replacement costs (Smith, Al-Mamun & Gröhn, 2017). The US dairy industry losses up to $200 per cow in MAP test-positive herds compared to MAP test-negative herds (Ott, Wells & Wagner, 1999). In 1996, USDA’s National Animal Health Monitoring System estimated that Johne’s disease costs the US dairy industry $250 million annually (Ott, Wells & Wagner, 1999). Testing blood and fecal samples from individual cows for MAP can be time consuming and cost prohibitive in large dairy herds. Environmental samples offer a convenient, cost-effective alternative to identify MAP infected dairy herds (Berghaus et al, 2006; Aly et al, 2012). Environmental samples that can be tested for MAP include fecal slurry on freestall pen floors, boot swabs or a combination of both (Donat et al, 2016; Hahn et al, 2017)
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